Electrically Dormant Sinoatrial Nodal Cells (SANC) are Awakened by Increased Camp-Dependent Phosphorylation of Coupled-Clock Proteins

Tsutsui, Kenta; Kim, Mary S.; Wirth, Ashley; Monfredi, Oliver; Ziman, Bruce D.; Byshkov, Rostislav; Maltsev, Alexander; Maltsev, Victor A.; Lakatta, Edward G.

doi:10.1016/j.bpj.2016.11.2181

Cited by 3 publications

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“…We have also recently observed similar non-AP-firing behaviours in a population of enzymatically isolated guinea pig and human SAN cells: these cells have LCRs but do not fire APs (36,37). A large population of these dormant isolated SAN cells begin to fire spontaneous APs in response to increases in intracellular cAMP (36,38). Such dormant cell behaviour within SAN tissue can potentially contribute to pacemaker function via (i) having a role in entrainment of oscillators that are heterogeneous 105 and is also made available for use under a CC0 license.…”

Section: Ca 2+ Signals Within Cells Embedded Within Hcn4 Meshwork Are Highly Heterogeneous In Spatial Distribution Amplitude Frequency Anmentioning

confidence: 56%

Synchronized Cardiac Impulses Emerge From Heterogeneous Local Calcium Signals Within and Among Cells of Pacemaker Tissue

Bychkov

Juhaszova

Tsutsui

et al. 2020

JACC: Clinical Electrophysiology

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184

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Background The current paradigm of Sinoatrial Node (SAN) impulse generation: (i) is that full-scale action potentials (APs) of a common frequency are initiated at one site and are conducted within the SAN along smooth isochrones; and (ii) does not feature fine details of Ca 2+ signalling present in isolated SAN cells, in which small subcellular, subthreshold local Ca 2+ releases (LCRs) self-organize to generate cell-wide APs.Objectives To study subcellular Ca 2+ signals within and among cells comprising the SAN tissue. MethodsWe combined immunolabeling with a novel technique to detect the occurrence of LCRs and AP-induced Ca 2+ transients (APCTs) in individual pixels (chonopix) across the entire mouse SAN images. ResultsAt high magnification, Ca 2+ signals appeared markedly heterogeneous in space, amplitude, frequency, and phase among cells comprising an HCN4 + /CX43cell meshwork.The signalling exhibited several distinguishable patterns of LCR/APCT interactions within and among cells. Apparently conducting rhythmic APCTs of the meshwork were transferred to a truly conducting HCN4 -/CX43 + network of straited cells via narrow functional interfaces where different cell types intertwine, i.e. the SAN anatomical/functional unit. At low magnification, the earliest APCT of each cycle occurred within a small area of the HCN4 meshwork and subsequent APCT appearance throughout SAN pixels was discontinuous. ConclusionsWe have discovered a novel, microscopic Ca 2+ signalling paradigm of SAN operation that has escaped detection using low-resolution, macroscopic tissue isochrones employed in prior studies: APs emerge from heterogeneous subcellular subthreshold Ca 2+ 105 and is also made available for use under a CC0 license.

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Section: Ca 2+ Signals Within Cells Embedded Within Hcn4 Meshwork Are Highly Heterogeneous In Spatial Distribution Amplitude Frequency Anmentioning

confidence: 56%

Synchronized Cardiac Impulses Emerge From Heterogeneous Local Calcium Signals Within and Among Cells of Pacemaker Tissue

Bychkov

Juhaszova

Tsutsui

et al. 2020

JACC: Clinical Electrophysiology

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184

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“…We have also recently observed similar non-AP-firing behaviours in a population of enzymatically isolated guinea pig and human SAN cells: these cells have LCRs but do not fire APs [34,35]. A large population of these dormant isolated SAN cells begin to fire spontaneous APs in response to increases in intracellular cAMP [34,36]. Such dormant cell behaviour within SAN tissue can potentially contribute to pacemaker function via (i) having a role in entrainment of oscillators that are heterogeneous both in phase and amplitude to self-organize into synchronized signals that underlie rhythmic impulse that emanate from the SAN; and (ii) their recruitment to fire APs in response to adrenergic receptor activation or AP silencing in response to cholinergic receptor stimulation.…”

Section: Some San Cells Have Lcrs But Do Not Fire Apsmentioning

confidence: 73%

Synchronized cardiac impulses emerge from multi-scale, heterogeneous local calcium signals within and among cells of heart pacemaker tissue

Bychkov

Juhaszova

Tsutsui

et al. 2020

Preprint

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The current functional paradigm of sinoatrial node (SAN), the heart's natural pacemaker, postulates the entrainment of full-scale action potentials (APs) at one common frequency and does not involve any subcellular events or subthreshold signals. SAN cells studied in isolation, however, generate subcellular, spontaneous, rhythmic, local Ca 2+ releases (LCRs) and, while each LCR is a small, subthreshold signal, the emergent LCR ensemble signal critically contributes to generation of spontaneous APs and accounts for the heterogeneity of AP firing rates of these cells.We hypothesized that cells embedded in SAN tissue also generate heterogeneous subthreshold LCR signals of different rates and amplitudes and that self-organization of the LCRs within and among cells critically contributes to the ignition of APs that emerge from the SAN to excite the heart. To this end we combined immunolabeling with a novel technique to image microscopic Ca 2+ dynamics, including both LCRs and AP-induced Ca 2+ transients (APCTs) within and among individual pacemaker cells across the entire mouse SAN.Immunolabeling identified a meshwork of HCN4(+)/CX43(-) non-striated cells of different morphologies that extended along the crista terminalis from the superior vena cava to the inferior vena cava, becoming intertwined with a network of striated cells, rich in F-actin and CX43, but devoid of HCN4 immunolabeling. The earliest APCTs within a given pacemaker cycle occurred within a small area of HCN4 meshwork below the superior vena cava, just medial to the crista terminalis. Although subsequent APCT appearance throughout the SAN at low magnification resembled a continuous propagation pattern, higher magnification imaging revealed that APCT appearance at different sites within the SAN was patchy and discontinuous. Both LCR dynamics and APCTs were markedly heterogeneous 3 in amplitudes and frequencies among SAN cells: in some cells, APCT occurrence was preceded by diastolic LCRs occurring in the same cell; other cells did not generate spontaneous APCTs, but had subthreshold LCRs only, which preceded APCT generation by adjacent cells; APCTs of various frequencies were generated steadily or in bursts.In summary, we discovered a novel, microscopic Ca 2+ signalling paradigm of SAN operation that could not be detected with low-resolution, macroscopic tissue methods employed in prior studies: synchronized macroscopic signals within the SA node, including full-scale APs, emerge from heterogeneous microscopic subthreshold Ca 2+ signals. This multiscale, complex process of impulse generation within the SAN resembles the emergence of organized signals from heterogeneous local signals generated within clusters of neurons within neuronal networks.

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“…1B). Next, SA node-residing atrial cells have a resting membrane potential between −70 and −80 mV [8], whereas our pilot measurements showed that dormant cells exhibit a resting membrane potential of about −35 mV [9]. In the presence of βAR stimulation, some dormant cells gained automaticity (Fig.…”

Section: Resultsmentioning

confidence: 99%

Heterogeneity of calcium clock functions in dormant, dysrhythmically and rhythmically firing single pacemaker cells isolated from SA node

et al. 2018

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Current understanding of how cardiac pacemaker cells operate is based mainly on studies in isolated single sinoatrial node cells (SANC), specifically those that rhythmically fire action potentials similar to the in vivo behavior of the intact sinoatrial node. However, only a small fraction of SANC exhibit rhythmic firing after isolation. Other SANC behaviors have not been studied. Here, for the first time, we studied all single cells isolated from the sinoatrial node of the guinea pig, including traditionally studied rhythmically firing cells ('rhythmic SANC'), dysrhythmically firing cells ('dysrhythmic SANC') and cells without any apparent spontaneous firing activity ('dormant SANC'). Action potential-induced cytosolic Ca transients and spontaneous local Ca releases (LCRs) were measured with a 2D camera. LCRs were present not only in rhythmically firing SANC, but also in dormant and dysrhythmic SANC. While rhythmic SANC were characterized by large LCRs synchronized in space and time towards late diastole, dysrhythmic and dormant SANC exhibited smaller LCRs that appeared stochastically and were widely distributed in time. β-adrenergic receptor (βAR) stimulation increased LCR size and synchronized LCR occurrences in all dysrhythmic and a third of dormant cells (25 of 75 cells tested). In response to βAR stimulation, these dormant SANC developed automaticity, and LCRs became coupled to spontaneous action potential-induced cytosolic Ca transients. Conversely, dormant SANC that did not develop automaticity showed no significant change in average LCR characteristics. The majority of dysrhythmic cells became rhythmic in response to βAR stimulation, with the rate of action potential-induced cytosolic Ca transients substantially increasing. In summary, isolated SANC can be broadly categorized into three major populations: dormant, dysrhythmic, and rhythmic. We interpret our results based on simulations of a numerical model of SANC operating as a coupled-clock system. On this basis, the two previously unstudied dysrhythmic and dormant cell populations have intrinsically partially or completely uncoupled clocks. Such cells can be recruited to fire rhythmically in response to βAR stimulation via increased rhythmic LCR activity and ameliorated coupling between the Ca and membrane clocks.

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Electrically Dormant Sinoatrial Nodal Cells (SANC) are Awakened by Increased Camp-Dependent Phosphorylation of Coupled-Clock Proteins

Cited by 3 publications

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Synchronized Cardiac Impulses Emerge From Heterogeneous Local Calcium Signals Within and Among Cells of Pacemaker Tissue

Synchronized Cardiac Impulses Emerge From Heterogeneous Local Calcium Signals Within and Among Cells of Pacemaker Tissue

Synchronized cardiac impulses emerge from multi-scale, heterogeneous local calcium signals within and among cells of heart pacemaker tissue

Heterogeneity of calcium clock functions in dormant, dysrhythmically and rhythmically firing single pacemaker cells isolated from SA node

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